How to calculate gas mileage
MPG = miles driven ÷ gallons used
Fill the tank, reset the trip meter (or note the odometer). Drive normally for at least half a tank, then refill. Divide miles driven by gallons to refill = your MPG. For accuracy, average over several tanks.
Example
- Trip distance: 280 miles
- Gallons to refill: 10
- MPG: 280 ÷ 10 = 28 MPG
- Cost per mile at $3.50/gal: $3.50 ÷ 28 = $0.125/mile
Average MPG by vehicle type
| Vehicle type | Typical MPG |
|---|---|
| EV (MPGe) | 100–130 MPGe |
| Plug-in hybrid (PHEV) | 50–100 MPGe |
| Hybrid (Prius, RAV4) | 40–55 MPG |
| Compact (Civic, Corolla) | 30–35 MPG |
| Sedan (Camry, Accord) | 25–32 MPG |
| Small SUV (CR-V, RAV4) | 25–30 MPG |
| Mid-size SUV | 20–25 MPG |
| Large SUV / 3-row | 17–22 MPG |
| Pickup truck (F-150, Silverado) | 18–22 MPG |
| Heavy-duty truck | 12–18 MPG |
| Sports car | 15–22 MPG |
Tips to improve gas mileage
- Check tire pressure monthly — every 1 PSI below recommended costs 0.2% MPG. Properly inflated tires save $0.10/gal equivalent.
- Drive 55–65 mph on highways — aerodynamic drag doubles going from 55 to 75 mph. Saves 15–20%.
- No idling — 10 seconds of idling uses more fuel than restarting. Turn off engine for stops over 30 seconds.
- Remove excess weight — every 100 lbs reduces MPG by 1–2%. Clean out the trunk.
- Remove roof racks when not in use — cargo boxes on top cost 10–25% MPG at highway speeds.
- Use cruise control on flat highways — maintains steady speed, improving efficiency.
- Accelerate smoothly — jackrabbit starts can cut MPG by 30%. Coast to red lights.
- Combine errands — cold starts use extra fuel. One longer trip is more efficient than many short ones.
- Keep up with maintenance — clean air filter, fresh oil, working O2 sensor all matter.
MPG vs liters per 100km
The US and UK use miles per gallon; most other countries use liters per 100 km (lower is better). They're inverses:
L/100km = 235.21 ÷ MPG
Quick reference: 25 MPG = 9.4 L/100km, 30 MPG = 7.8 L/100km, 40 MPG = 5.9 L/100km, 50 MPG = 4.7 L/100km. Note: UK gallons are 20% larger than US gallons (4.55L vs 3.79L), so 30 UK MPG = 25 US MPG.
Cost per mile at various gas prices
| MPG | $3.00 | $3.50 | $4.00 | $4.50 |
|---|---|---|---|---|
| 15 MPG | $0.200 | $0.233 | $0.267 | $0.300 |
| 20 MPG | $0.150 | $0.175 | $0.200 | $0.225 |
| 25 MPG | $0.120 | $0.140 | $0.160 | $0.180 |
| 30 MPG | $0.100 | $0.117 | $0.133 | $0.150 |
| 35 MPG | $0.086 | $0.100 | $0.114 | $0.129 |
| 40 MPG | $0.075 | $0.087 | $0.100 | $0.113 |
| 50 MPG | $0.060 | $0.070 | $0.080 | $0.090 |
Annual fuel cost comparison (12,000 miles, $3.50/gal)
| Vehicle type | MPG | Annual cost |
|---|---|---|
| Heavy-duty truck | 15 | $2,800 |
| Large SUV | 19 | $2,211 |
| Pickup truck | 20 | $2,100 |
| Sedan | 28 | $1,500 |
| Compact car | 32 | $1,313 |
| Hybrid | 45 | $933 |
| Plug-in hybrid | 70 | $600 |
| EV (MPGe at elec rates) | 115 | $520 |
EV cost based on ~3.5 mi/kWh at $0.16/kWh electricity — actual cost varies by local rates.
Frequently asked questions
How do I calculate my car's gas mileage?
Fill the tank, note the odometer reading (or reset the trip meter). Drive until the tank is half empty or lower, then fill up again. MPG = miles driven ÷ gallons used to refill. Example: drove 280 miles, used 10 gallons to refill = 28 MPG. For accuracy, calculate over several tanks. Many modern cars show real-time and average MPG in the dashboard display.
What is good gas mileage?
For most cars: 30+ MPG combined is excellent, 25–30 is good, 20–25 is average, below 20 is poor for a passenger car (but normal for trucks and SUVs). The EPA rates vehicles with a combined city/highway MPG. The US national average fleet is about 25 MPG. Hybrids average 45–55 MPG; EVs rate 100+ MPGe (miles per gallon equivalent). Your real-world MPG is usually 10–15% lower than the EPA sticker.
How much does it cost to drive 100 miles?
Divide 100 by your MPG, then multiply by gas price. At 25 MPG with $3.50 gas: 100 ÷ 25 × $3.50 = $14. At 30 MPG: $11.67. At 20 MPG: $17.50. At 15 MPG: $23.33. For an EV at roughly 3.5 mi/kWh and $0.16/kWh: 100 ÷ 3.5 × $0.16 = $4.57 — about a third the cost of gas. Our calculator handles any MPG and gas price.
How do I calculate fuel cost for a trip?
Fuel cost = (trip distance ÷ MPG) × gas price per gallon. For a 500-mile trip at 28 MPG with $3.50 gas: (500 ÷ 28) × $3.50 = 17.86 gal × $3.50 = $62.50. For round trips, double the distance or use our round-trip toggle. Add 10% for real-world variance (city driving, traffic, AC use).
Does AC use more gas?
Yes, running the AC reduces fuel economy by 3–10% depending on outside temperature and speed. At highway speeds, AC is typically more efficient than open windows (which create aerodynamic drag). At city speeds under 40 mph, windows-down is slightly more efficient. AC effects are larger in small engines — a compact car may lose 10–15% MPG running AC on a hot day; large V8s barely notice.
Why is my gas mileage getting worse?
Common causes: (1) Low tire pressure — reduces MPG 0.2% per PSI below recommended, (2) Dirty air filter, (3) Old spark plugs or O2 sensor, (4) Dragging brakes, (5) Worn oxygen sensor, (6) Short trips and cold starts (engine needs time to reach optimal temperature), (7) Aggressive driving (rapid acceleration costs 15–30% MPG), (8) Wrong oil viscosity. Check tire pressure monthly and follow maintenance schedule.
What is the difference between MPG and MPGe?
MPG is miles per gallon of gasoline — a direct efficiency measure for gas vehicles. MPGe (MPG equivalent) applies to electric and alternative-fuel vehicles: it converts electricity (or other fuel) to the equivalent gasoline energy. 33.7 kWh = 1 gallon of gasoline in energy terms. A Tesla Model 3 at 134 MPGe means it uses as much energy to go 134 miles as a gas car using 1 gallon. MPGe ignores cost differences — electricity per kWh is usually much cheaper than gas per gallon.
How many gallons does it take to drive 500 miles?
Divide 500 by your MPG. At 25 MPG: 20 gallons. At 28 MPG: 17.9 gallons. At 32 MPG: 15.6 gallons. At 35 MPG: 14.3 gallons. At $3.50/gal: 25 MPG costs $70, 35 MPG costs $50 — the difference over many trips adds up. Highway MPG is typically higher than city MPG for internal combustion cars.
Does driving speed affect gas mileage?
Yes, significantly. Most cars peak at 45–60 mph. Above 60 mph, aerodynamic drag increases rapidly: going 75 mph vs 55 mph can reduce MPG by 15–20%. Rule of thumb: every 5 mph over 60 is like paying an extra $0.25/gal for gas. Use cruise control at moderate speeds for best efficiency. City driving (stop-and-go) is typically 20–30% less efficient than highway.
How do I convert MPG to liters per 100km?
Formula: L/100km = 235.21 ÷ MPG. Examples: 25 MPG = 9.4 L/100km, 30 MPG = 7.8, 35 MPG = 6.7, 40 MPG = 5.9, 50 MPG = 4.7. MPG and L/100km are inverse — higher MPG equals lower L/100km. Most countries use L/100km; US and UK still use MPG (but UK gallons are 20% larger than US gallons!).